1. Technical Field
The invention relates to bioprosthetic heart valves and the treatment of valvular heart disease.
2. Background Information
The heart is a hollow, muscular organ that circulates blood throughout an animal""s body by contracting rhythmically. In mammals, the heart has four-chambers situated such that the right atrium and ventricle are completely separated from the left atrium and ventricle. Normally, blood flows from systemic veins to the right atrium, and then to the right ventricle from which it is driven to the lungs via the pulmonary artery. Upon return from the lungs, the blood enters the left atrium, and then flows to the left ventricle from which it is driven into the systematic arteries.
Four main heart valves prevent the backflow of blood during the rhythmic contractions: the tricuspid, pulmonary, mitral, and aortic valves. The tricuspid valve separates the right atrium and right ventricle, the pulmonary valve separates the right atrium and pulmonary artery, the mitral valve separates the left atrium and left ventricle, and the aortic valve separates the left ventricle and aorta. Generally, patients having an abnormality of a heart valve are characterized as having valvular heart disease.
A heart valve can malfunction either by failing to open properly (stenosis) or by leaking (regurgitation). For example, a patient with a malfunctioning aortic valve can be diagnosed with either aortic valve stenosis or aortic valve regurgitation. In either case, valve replacement by surgical means is a possible treatment. Replacement valves can be autografts, allografts, or xenografts as well as mechanical valves or valves made partly from pig valves. Interestingly, cryopreserved allografts remain viable within the recipient patient for many years after transplantation. Unfortunately, replacement valves are susceptible to problems such as degeneration, thrombosis, and calcification.
The invention involves methods and materials related to heart valves and the treatment of valvular heart disease. Specifically, the invention provides heart valve cells and heart valve cusps as well as methods for making heart valves. The invention also provides methods and materials for (1) slowing heart valve degeneration, thrombosis, and calcification, (2) treating carcinoid heart disease, (3) identifying inhibitors of heart valve degeneration, thrombosis, and calcification, and (4) determining the safety of drugs.
The invention is based on the discovery that heart valve cells expressing a polypeptide having nitric oxide synthase activity do not exhibit characteristics indicative of heart valve calcification and degeneration. Specifically, heart valve cells containing nucleic acid that encodes a polypeptide having nitric oxide synthase activity exhibit, in response to a valvular heart disease-promoting stimulus, a different extracellular matrix profile than that exhibited by similar cells lacking that nucleic acid. The molecular makeup of a heart valve""s extracellular matrix can be an important factor that determines the degree of heart valve calcification and degeneration. For example, significant expression of osteopontin, a polypeptide abundant in bone matrix, can lead to significant tissue calcification. Heart valve cells containing nucleic acid that encodes a polypeptide having nitric oxide synthase activity also exhibit, in response to a valvular heart disease-promoting stimulus, less proliferation and apoptosis than the proliferation and apoptosis exhibited by similar cells lacking that nucleic acid. The level of heart valve cell proliferation and apoptosis can correlate with the degree of heart valve calcification and degeneration. For example, significant proliferation and apoptosis of heart valve cells can lead to heart valve thickening, and thus heart valve malfunction and degeneration. It is noted that tissue thickening occurs presumably because cell proliferation out paces apoptosis over time. The heart valve cells and cusps described herein can be used to make bioprosthetic heart valves having a reduced susceptibility or prolonged resistance to degeneration, thrombosis, and calcification. Clearly, such bioprosthetic heart valves would be useful in any type of heart valve replacement procedure.
The invention also is based on the discovery that serotonin receptor antagonists (e.g., 5HT1B receptor antagonists) can inhibit serotonin-induced proliferation of heart valve cells from patients diagnosed with carcinoid heart disease. Thus, serotonin receptor antagonists can be used to treat carcinoid heart disease. Further, the methods and materials used to identify serotonin receptor antagonists as a treatment for carcinoid heart disease also can be used to identify drugs for the treatment of other valvular heart diseases as well as test the safety of any drug designed for human use. Clearly, identifying new valvular heart disease treatments and determining drug safety in general will greatly improve overall human health care.
In general, one aspect of the invention features a non-murine heart valve cell (e.g., an endothelial cell or myocyte) containing an exogenous nucleic acid that encodes a polypeptide having nitric oxide synthase activity (e.g., endothelial nitric oxide synthase).
In another embodiment, the invention features an isolated heart valve cusp where a cell of the cusp contains an exogenous nucleic acid that encodes a polypeptide having nitric oxide synthase activity (e.g., endothelial nitric oxide synthase). The cell can be a porcine or human cell.
Another embodiment of the invention features a method for making a bioprosthetic heart valve. The method includes obtaining a heart valve cusp and introducing nucleic acid into a cell of the cusp, where the nucleic acid encodes a polypeptide having nitric oxide synthase activity (e.g., endothelial nitric oxide synthase). The cell can be a porcine or human cell. The nucleic acid can be introduced into the cell via adenoviral-mediated nucleic acid transfer. The nucleic acid can be integrated into the genome of the cell. The method can include fixing the cusp, and the fixation step can occur after the introduction step. The method can include freezing the cusp, and the freezing step can occur after the introduction step.
In another aspect, the invention features a method for slowing the degeneration of a heart valve within a non-murine mammal. The method includes introducing nucleic acid encoding a polypeptide having nitric oxide synthase activity into a cell of the heart valve such that the polypeptide is expressed. The introduction step can be performed in vitro. The heart valve can be an autograft, allograft, or xenograft. The method can include administering an inhibitor of hydroxymethylglutaryl coA reductase activity to the mammal. The inhibitor can be pravastatin, atorvastatin, simvastatin, or lovastatin.
In another embodiment, the invention features a method for slowing heart valve degeneration. The method includes identifying a mammal at risk of developing heart valve degeneration, and administering an inhibitor of hydroxymethylglutaryl coA reductase activity to the mammal. The mammal can contain a heart valve replacement. The mammal can have congenital valvular disease or bicuspid valvular disease.
Another aspect of the invention features a method for treating carcinoid heart disease in a mammal. The method includes administering a serotonin receptor antagonist to the mammal. The antagonist can be specific for a 5HT1B receptor. The antagonist can contain a xcex2-blocker. The antagonist can be pindolol.
Another aspect of the invention features a method for identifying an inhibitor of heart valve degeneration. The method includes contacting heart valve cells with a stimulant such that the cells proliferate, contacting the cells with a test compound, and determining if the test compound reduced the proliferation of the cells, where the reduction of proliferation indicates that the test compound is an inhibitor of heart valve degeneration.
In another embodiment, the invention features a method for determining the safety of a drug. The method includes contacting heart valve cells with the drug, and determining if the drug induced proliferation of the cells, where the induction of proliferation indicates that the drug promotes heart valve degeneration.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.
Other features and advantages of the invention will be apparent from the following detailed description, and from the claims.